The way ships work in the astral sea is they have an air bubble with a gravity plane. In the astral sea you move with INT. If I enter the air bubble with enough speed, could I feasibly carpet bomb the ship in an arc.
I heard D&D doesn't have proper physics, and that falling is up to a maximum of 500 ft per turn. So theoretically with enough horizontal momentum would this be possible?
As mentioned, the rules as written do not support your neat idea, due to their simplistic nature: as soon as you enter a gravity field, you fall straight "down", up to 500 ft. per round if using Xanathar's rules, unless you have a Fly speed.
If you have access to flight, you could use. Even the most restrictive options -- a Fly Speed only on your turn, a few turns/day -- would be sufficient for your stunt.
A Glide ability, such as the Hadozee's, allows a character to move horizontally while falling. Depending on how much movement Glide allows, it could get tricky, but with a high enough Int your character should be able to compute a trajectory that allows them to exit the bubble by Gliding.
I shall note that your character could execute a FlyBy by staying outside of the bubble of gravity altogether, and throwing things in. The things thrown, once caught in the bubble of gravity, would fall towards the center.
Your DM would have to work out the effect on targeting; but for carpet-bombing precision may not be that much of a problem.
A larger issue with your plan is the idea of carpet-bombing. D&D 5.0 only offers limited Object Interactions.
For example, the rules for Caltrops mention:
As an action, you can spread a bag of caltrops to cover a square area that is 5 feet on a side.
So, 5 ft. x 5 ft. area per turn.
Rules for throwing vials of acid, etc... tend to have similar wording, and you only have 1 Object Interaction (as Free Action) on top to drop an object (if within the bubble of gravity).
If several characters do the fly-by, they can each throw / drop an object.
There are many spells with an area of effects, and some objects too. If you want a large area of effect, I'd advise into looking into those. Fireball, whether innate, by wand, or by scroll, would "carpet bomb" a large area.
As is often mentioned, D&D is not a physics simulation, and this question is a good example for why: if you assumed the rules supported Newtonian physics, you would now need to calculate the requirements for speed, gravity, mass of the wizard to resolve answering this question.
Do Newtonian physics allow such slingshots? Yes they do. Should you expect players and DM to stop their play session to try and calculate this with differential equations or whatever the appropriate framework would be here? Of course not.
This is the reason why the rules simplify, and the movement rules do not involve momentum or acceleration or friction — to avoid dealing with sich complications.
In the core rules you immediately fall all the way, if you fall, or 500 feet per round when using Xanathar‘s optional rules.
So, if you had no fly speed, then you would fall to the plane of gravity as soon as you entered the bubble. If you had a fly speed, you could normally move up to your speed through the air of the bubble.
If you and your group enjoy working out advanced physics problems in your spare time, your DM is free to overrule the rules and allow you to do this, in case you can demonstrate it would work.
There is no such thing as momentum in D&D.
Your DM might be willing to house rule this.
